I have an I/O Trim switch problem..... Mercruiser 4.3L Alpha One Drive

Sometimes my Trim switch on the control handle works and raises the I/O drive, sometimes it doesn't ? Problem seems to be intermittent ?

There have been situations where I've got back to the boat ramp to take my boat out of the water, only to find the Trim doesn't raise the I/O. In these instances, I have to use the 'trailer' switch button to raise the I/O. The 'trailer button', is on the same control handle.

Any ideas ?

Thanks !